Department of Chemistry, Shiraz University, Adabiat Four-way, Shiraz, Fars 71454, Iran.
Spectrochim Acta A Mol Biomol Spectrosc. 2010 Jan;75(1):340-6. doi: 10.1016/j.saa.2009.10.037. Epub 2009 Oct 31.
The acidity constants of some newly synthesized Schiff base derivatives were determined by hard-model based multivariate data analysis of the spectrophotometric data in the course of pH-metric titration in 50% (v/v) methanol-water binary solvent. The employed data analysis method was also able to extract the pure spectra and pH-dependent concentration profiles of the acid-base species. The molecules that possess different substituents (both electron donating and withdrawing) on the ortho-, meta- and para-positions of one of the phenyl ring showed variable acidity constants ranging from 8.77 to 11.07 whereas the parent molecule had an acidity constant of 10.25. To investigate the quantitative effects of changing of substitution pattern on the acidity constant, a quantitative structure-property relation analysis was conducted using substituent constants and molecular descriptor. Some models with high statistical quality (measured by cross-validation Q(2)) were obtained. It was found that the acidity constant of the studied molecules in the methanol-water mixed solvent not only is affected by electronic features of the solutes but also by the lipophilic interaction between methanol part of solvent and the deprotonated solutes.
采用硬模型多元数据分析方法，对在 50%（v/v）甲醇-水二元溶剂中进行 pH 滴定过程中的分光光度数据进行分析，确定了一些新合成的希夫碱衍生物的酸度常数。所采用的数据分析方法还能够提取酸碱物种的纯光谱和与 pH 相关的浓度分布。在苯环的邻位、间位和对位上具有不同取代基（供电子和吸电子）的分子表现出可变的酸度常数，范围从 8.77 到 11.07，而母体分子的酸度常数为 10.25。为了研究取代模式变化对酸度常数的定量影响，使用取代常数和分子描述符进行了定量构效关系分析。得到了一些具有较高统计质量（通过交叉验证 Q(2) 测量）的模型。结果表明，在甲醇-水混合溶剂中研究分子的酸度常数不仅受溶质的电子特性影响，还受溶剂甲醇部分与去质子化溶质之间的亲脂相互作用影响。
